The present invention relates to an oxygen absorbent. In more particular, it relates to a novel oxygen absorbent comprising boron or a reducing boron compound as the major constituent.
The term "oxygen absorbent" used in the present specification and claims refers to a substance which has functions of absorbing oxygen and also absorbing moisture and acidic substances and exerts such useful effects in storing various goods as disinfection, mildew-proofing, insect proofing, and prevention of oxidation, fading, discoloration and rusting, etc. by removing oxygen, moisture and acidic substances from the atmosphere surrounding said oxygen absorbent. It is usually employed to mean an oxygen absorbent composition having the above-mentioned functions and effects but sometimes employed in the sense of a parcel containing the oxygen absorbent composition. A rate of absorbing oxygen in said oxygen absorbent is accelerated by maintaining in advance water.
One of the techniques employed for storage of foods, etc. is the use of an oxygen absorbent. This technique comprises placing an oxygen absorbent together with foods etc. in a hermetically sealed bag or a tightly closed container (hereinafter sometimes referred to simply as a sealed container or a container) with gas barrier property to make the atmosphere in the sealed container substantially free from oxygen and thereby to inhibit the oxidation of foods etc. and the growth or proliferation of bacteria and mildew, and is used in storing a vast variety of foods, etc. Oxygen absorbents used so far are those which comprise iron powders as the major constituent for reasons of oxygen absorbing capacity, ease of handling, safety, cost, and so forth.
In the case of packaged foods, for example, it is a common practice, after the foods have been hermetically sealed in a packaging bag, to inspect the package with a metal detector in order to check contamination by foreign matter.
However, said oxygen absorbent comprising iron powders as the major constituent is naturally detected by the metal detector, so that the metal detector test cannot be applied to food packages etc. having the oxygen absorbent enclosed therein.
As for corrosion inhibition techniques for metals and metallic articles, there have so far been known the use of corrosion preventive oils, volatile corrosion inhibitors, volatile corrosion inhibitive paper, etc., and these methods are described as "the general rules for corrosion preventive packaging" in JIS Z 0303-1035.
However, these methods are featured by coating or spraying onto the metal surface substances which have a corrosion preventive effect, so that they cannot be used for metals and metallic articles which should be desirably kept away from the contact with such substances, e.g., reagents, electronic parts and semiconductors.
It is frequently practiced to seal a metallic article together with a desiccant, such as silica gel, in a packaging material having a low gas permeability and moisture permeability to effect corrosion inhibition. Such a method is, for example, provided for as "silica gel desicant for packaging" in JIS Z 0701-1977. This method, however, merely reduces the relative humidity in the sealed container by the use of a desiccant and can give only an effect of retarding the rust formation due to oxidation.
Another corrosion inhibition technique for metals, which uses an oxygen absorbent, is disclosed in Japanese Patent Application Kokoku (Post-Exam. Publn.) No. 62-040,880. It comprises enclosing a metal or metallic article in a gas barrier packaging material together with a parcel formed by filling an oxygen absorbent into a gas-permeable packaging material, to produce a substantially oxygen-free condition in the sealed enclosure and thereby to effect the corrosion inhibition of the metal.
Many proposals have already been made regarding the substances used as the oxygen absorbent. There have been known, for example, those which comprises as the major constituent sulfites, catechol, ascorbic acid and/or its salts, or metal powders.
However, the above-mentioned oxygen absorbents require water to absorb oxygen and hence absorbents used in practice contain water therein. Said water may evaporate from the oxygen absorbent to increase the relative humidity in the closed system and often to cause rusting in spite of the substantially oxygen-free condition kept in the system.
Further, when the oxygen absorbent, or the metallic article to be stored itself, produces an acidic gas, the acidic gas may greatly promote rust formation.
As described above, although a corrosion inhibitor which has an oxygen absorbing function, a drying function and further, desirably, a function of absorbing an acidic gas in combination has been awaited for corrosion inhibition of metals and metallic articles, the products of the prior art are all insufficient in some of these functions and are not satisfactory for use as a corrosion inhibitor.